In the past, silicone rubber laminates comprising a conductive silicone rubber containing carbon black and a dielectric silicone rubber stacked thereon were widely used as electric contact material for electric and electronic parts, typically zebra connectors and contact rubber.
For the manufacture of these silicone rubber laminates comprising a conductive silicone rubber containing carbon black and a dielectric silicone rubber stacked thereon, a number of proposals have been made with respect to the compositions of conductive and dielectric silicone rubber layers as well as the laminate manufacturing method. For example, Japanese Patent Publication No. 41417/1981 discloses a method including curing a conductive carbon black-containing silicone rubber with organic peroxides to form a conductive cured silicone rubber layer, stacking a second uncured silicone rubber layer thereon, and curing the second layer with organic peroxides. Japanese Patent Publication No. 34982/1986 discloses an integrated silicone rubber article, and a method for making the same, including a cured mass of silicone rubber containing 5 to 75% by weight of carbon black and a cured mass of a carbon black-free silicone rubber composition. The carbon black-free silicone rubber predominantly comprises an organopolysiloxane having at least two alkenyl groups per molecule, an organohydrogenpolysiloxane, and a reinforcing silica filler. The molar ratio of the SiH group in the organohydrogenpolysiloxane to the alkenyl group in the organopolysiloxane being from 0.8/1 to 6/1, and the silicone rubber composition being addition reaction curable in the presence of a platinum series catalyst. Japanese Patent Publication No. 39188/1986 discloses an integrated silicone rubber article, and a method for its preparation, that includes a cured mass of conductive silicone rubber containing 5 to 75% by weight of carbon black, the conductive silicone rubber being addition reaction curable in the presence of a platinum series catalyst, and a cured mass of substantially carbon black-free silicone rubber which is vulcanizable with non-acyl organic peroxides.
However, since the cured mass of conductive silicone rubber containing carbon black is covered with an uncured dielectric silicone rubber layer followed by curing, these silicone rubber laminates are weak in bond strength between the silicone rubber layers and less satisfactory in long term storage.
Often, these laminates are used as electric contact material in electronic devices. Few problems arise with respect to the bond between the conductive and dielectric silicone rubber layers if the electronic devices are used in an air conditioned environment. In the current days when electronic devices are used in any working environment, a problem can arise with respect to the bond between the conductive and dielectric silicone rubber layers, particularly in a hot humid environment. Therefore, there is a need to improve the bond between conductive and dielectric silicone rubber layers of a laminate such that the laminate may be fully reliable as an electric contact material as found in zebra connectors.